The present invention relates to a method for forming a photoresist pattern and a method for manufacturing a semiconductor device using the photoresist pattern forming method.
With the development of a micro-fabrication technique, improvements in performance of a semiconductor device and its high integration have recently been in progress. The development of a semiconductor device based on a 65-90 nm design rule is currently underway. With miniaturization of the semiconductor device, various factors to yield reductions are becoming manifest in its manufacturing process. As one of the factors to the yield reductions, may be mentioned, collapse of a photoresist pattern.
The photoresist pattern collapse frequently occurs in, for example, a fine photoresist pattern high in aspect ratio, which is formed in a gate forming process step or the like. The photoresist pattern collapse mainly occurs upon (1) a rinse step in a lithography process step and upon (2) a dry etching step executed after the lithography process step.
It has already been clarified that the photoresist pattern collapse at the rinse process step is attributable to surface tension generated when rinse liquid (pure water) existing between adjacent photoresist patterns is dried. As a countermeasure against to it, there has been disclosed a technique for adding isopropyl alcohol for reducing surface tension to the rinse pure water (refer to, for example, a patent document 1 (Japanese Unexamined Patent Publication No. H5(1993)-285972 (1st page and FIG. 4).
There has also been disclosed a technique for compressing a photoresist film in its thickness direction at the time of pre-bake of a photoresist applied onto the entire surface of a substrate to suppress the photoresist pattern collapse at a rinse step, and enhancing the density of the photoresist film thereby to increase the mechanical strength of the photoresist (refer to, for example, a patent document 2 (Japanese Unexamined Patent Publication No. H 11 (1999)-219886 (1st page)).
However, the methods according to the patent document 1 and the patent document 2 respectively show that they are effective in preventing the collapse of the photoresist pattern at the rinse step but do not suggest a method for solving the photoresist pattern collapse generated at the dry etching step, whose cause is not yet clear.